Drill Chuck Runout

[Parlo]

The threads on your arbor have sharp crests, this will contribute to the runout. The male threads are locating on their sharp points into the root radii in the female thread preventing engagement of the thread flanks. I would suggest removing these points when cutting any male thread before any final passes to size. Better still, use a full form insert.

 

[Eddyde]

Also, when tightening a chuck, use all three holes. Doing this will help both accuracy and grip.

 

[jakes_66]

The threads on your arbor have sharp crests, this will contribute to the runout. The male threads are locating on their sharp points into the root radii in the female thread preventing engagement of the thread flanks. I would suggest removing these points when cutting any male thread before any final passes to size. Better still, use a full form insert.

I'm super interested to see if this helps. I've learned so much from this forum, something new nearly every day. Thanks Parlo!!

 

[Chewy]

The threads on your arbor have sharp crests, this will contribute to the runout. The male threads are locating on their sharp points into the root radii in the female thread preventing engagement of the thread flanks. I would suggest removing these points when cutting any male thread before any final passes to size. Better still, use a full form insert.

Thanks! I will look into this. I hit the threads with a file and then recut at the last setting. Saw what looked like a burr, so I ran a thread file over them also. The arbor and a spare nut both threaded onto the shaft easily without slop, so I didn't look at them again. I will examine them with a magnifying glass on the permanent arbor.

I am waiting on replacement drill chuck before breaking down the setting. When I cut the permanent arbor, I will try all of the suggestions to see just how good the drill chuck can get. The current shimmed out reading of around .002 on the drill is OK. Now, can I do even better? Will let everyone know in a few days.

 

[Boxless]

Boxless, the grabbing pin in the jaws is a version of what Darkzero and Weldingrod1 is saying.

Yes, it is a version, but there is a difference. That difference is the quality and concentricity of the chuck you have on your lathe.

By that, I mean, you can put a gauge pin into your four jaw and indicate it to zero at some certain distance from the chuck. That will guarantee the AXIAL runout at that specific distance from the chuck. Even if the part is visibly crooked in the jaws, you can get it to indicate perfect at one location. But if you move away from that location (either closer to or farther from the chuck), it will no longer indicate concentric.

I've got one four jaw that holds shafts darn near perfect straight, but then I have another one which will only hold to about one thousandth per inch of travel. I've looked it over and can believe some of the jaws are worn a little uneven from front to back. I can chuck up a piece of nice ground 1/2 rod in that 4-jaw and indicate it to zero an inch from the chuck. But four inches from the chuck, I get a couple thousandths runout. The part does not stick straight out from that 4-jaw without fiddling.

So getting back to the beginning... Creating the stub upon which to grip with the drill chuck right there on the lathe should pretty much wash all of that kind of error out. And that's the difference between chucking up on a piece of ground gauge rod vs. making a short stub on the lathe to use as a test grabby.

 

[Boxless]

Oh, and about the surface finish, it doesn't look too good in the pic, but maybe it's just a trick of the camera.

Good luck with the project, and I hope you get your sub-thousandth you're looking for.

 

[Chewy]

Boxless, you are correct. That is the way I do my arbors and extensions. Also why the test shaft is still sitting in the lathe three days later.
I will drill, bore and ream 1/2" hole, 1-3/4 deep in a collet or chuck. Then flip and rough out the other side. Take to mill , drill & tap two set screws to tighten on motor shaft. Now I go back top lathe and clamp piece of round stock in and turn 1/2" shaft 1-1/2" as perfect as possible, no taper. I want an air tight sliding fit. Slide the arbor on and take very light cuts to dimension and threading. Center drill and tap screw hole. Done. If I don't screw up, everything will read almost 0, usually does.
It is extra work but beats even a collet for concentrically.